Group III nitrides are used as semiconductor films by which light-emitting semiconductor elements are formed, and in recent years there have been hopes for them as semiconductor films in semiconductor light-emitting elements constituting, in particular, high-luminance light sources for green light to blue light and also light sources for ultraviolet light and white light.
FIG. 1 is a block diagram showing one example of a conventional so-called PN type semiconductor light-emitting element.
In the semiconductor light-emitting element 10 shown in FIG. 1, the following are successively formed on a substrate 1, which is formed, for example, from a sapphire single crystal: a buffer layer 2 constituted by GaN, an underlayer 3 constituted by Si-doped n-GaN, an n-type electrically conductive layer 4 constituted by Si-doped n-AlGaN, a light-emitting layer 5, a p-type clad layer 6 constituted by Mg-doped p-AlGaN and a p-type electrically conductive layer 7 constituted by Mg-doped p-GaN.
The light-emitting layer 5 can be constituted as a single group III nitride layer or as a multiple-quantum-well (MQW) structure, and in recent years in particular it can also be constituted as a quantum dot structure. This quantum dot structure presents a structure in which, as, for example, shown in FIG. 2, crystals 12-1-12-5 in the form of islands constituted by GaInN are formed in a base layer 17 constituted by GaN. These insular structures may be mutually isolated or they may be connected to one another. The specific form of the insular structures depends on the conditions of their fabrication. In this example, the insular structures 12-1-12-5 are so constituted that they are mutually isolated.
A portion of the n-type conductive layer 3 is exposed and an Al/Ti or similar n-type electrode 8 is formed on this exposed portion, and, further, an Au/Ni or similar p-type electrode 9 is formed on the p-type conductive layer 7. The imposition of a set voltage across the n-type electrode 8 and the p-type electrode 9 results in recombination of carriers in the light-emitting layer 5 and emission of light of a set wavelength. This wavelength is determined by the light-emitting layer's structure and composition, etc.
In the semiconductor light-emitting element shown in FIG. 1, the underlayer 3 and the n-type conductive layer 4 constitute an n-type conductor layer group, while the p-type clad layer 6 and the p-type electrode 7 constitute a p-type conductor layer group.
In order to make practical use of the semiconductor light-emitting element shown in FIG. 1, it is necessary to place the semiconductor light-emitting element 10 in an atmosphere which does not contain hydrogen, and then give the p-type conductor layer group constituted by the p-type clad layer 6 and p-type electrode 7 an activation treatment by effecting a heating treatment at a temperature of 400° C. or more, and lower the resistance value to a set value, eg, by separating and removing the element hydrogen which has combined with the Mg which was added as a dopant (Japanese Patent No. 25407991).
However, when the light-emitting layer 5 is constituted as a quantum dot structure such as shown in FIG. 2, the activation treatment at such a high temperature sometimes causes a breakdown of the quantum dot structure. As a result, it is not possible to fabricate short-wavelength semiconductor light-emitting elements which can operate practical applications.
The object of the present invention is to provide a semiconductor light-emitting element which can serve in practical applications, and in which a p-type semiconductor layer group and an n-type semiconductor layer group are deposited on a set substrate, a quantum dot structure type light-emitting layer is provided between the p-type semiconductor layer group and the n-type semiconductor layer group, and the resistance of the p-type semiconductor layer group is lowered sufficiently, and to provide a substrate for this semiconductor light-emitting element. It is also an object to provide a method of fabricating this semiconductor light-emitting element.